The invention relates generally to semiconductor logic devices, and more specifically to domino logic circuitry having a novel NMOS precharge gate.
Semiconductor operational frequencies are ever increasing, requiring circuitry and processes that support these faster clock rates. Domino circuits have been used in such circuits to speed processing, due to the way in which a domino logic circuit handles data. A typical domino logic circuit receives data on a first transition of a clock, and couples a logically derived signal to external circuitry on a next transition of the clock.
A conventional domino circuit includes dynamic circuitry coupled to static gate circuitry. The dynamic circuitry pre-charges an input of the static circuitry when a clock signal is low, and couples an input data signal to the static circuitry when the clock signal is high. The dynamic circuitry often is n-type metal oxide semiconductor (NMOS) pull-down circuitry, that is operable to pull down the level of a relatively weakly held pre-charged circuit node. The node is then latched in static CMOS circuitry to provide a stable output until the next logical cycle.
But, the speed of such logic is limited by the time it takes to pre-charge the dynamic circuit node that provides the data signal to the static CMOS latch, and by the time it takes to pull down the weakly-held precharged node voltage to provide a low signal level to the latch. For these reasons and others that will be apparent to those skilled in the art upon reading and understanding this specification, a need exists for a domino logic circuit that reduces the time required to operate the dynamic pre-charge portion of a domino logic circuit.
A domino logic circuit is provided. The circuit includes an n-channel clock transistor coupled between a dynamic output node and a high voltage connection, the gate of the clock transistor further coupled to receive an inverse clock signal. A first inverter and a second inverter are connected in series such that the input of the first inverter is connected to the output of the second inverter. The input of the second inverter is connected to the dynamic output node. An n-channel level keeper transistor is connected between the dynamic output node and the high voltage connection, and the gate of the level keeper transistor is connected to the output of the first inverter. A pull-down circuit is connected between the dynamic output node and a low-voltage connection.